As a technique to improve an output of an engine, a method (supercharging) of compressing intake air with a supercharger and supplying an engine with the compressed intake air is known, and widely used in an engine for an automobile and the like. A supercharger may transitionally enter an abnormal operational state with surging, over-speed, or the like, depending on the operational state of the supercharger. Such abnormal operation may lead to breakage of various devices, and thus needs to be prevented as much as possible.
Patent Document 1 discloses an invention, as a control device for a turbocharger, for suppressing surging by predicting occurrence of surging from an operational state of the turbocharger and opening a waste-gate valve immediately before occurrence of surging to reduce a flow rate of exhaust gas flowing to a turbine.
Patent Document 2 discloses an invention, as a supercharging control device, for suppressing surging by providing a compressor-bypass valve for returning intake air from a downstream side toward an upstream side of a compressor and opening the bypass valve to return intake air if occurrence of surging is predicted.
Patent Document 3 discloses an invention, as a control device for a variable geometry turbocharger, for suppressing over-speed by changing a vane angle of nozzle vanes to achieve the maximum nozzle area during over-speed of a turbocharger.